1. Field of the Invention
The present invention relates to a semiconductor laser device and a method of designing the same.
2. Description of the Background Art
In recent years, semiconductor laser devices operable at a low operating current have been actively studied and developed. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL.1, NO.2, PP.102-109, 1995 has reported that in a real refractive index guided semiconductor laser employing a transparent current blocking layer, its operating current can be reduced.
In such a real refractive index guided semiconductor laser device, it is considered that a transverse mode is stabilized when a real refractive index difference is large to some extent. For example, in the above-mentioned document, the real refractive index difference is approximately 5.times.10.sup.-3.
In the above-mentioned real refractive index guided semiconductor laser device employing a transparent current blocking layer, however, it is difficult to make light output power higher in fundamental transverse mode lasing.
Furthermore, in the above-mentioned real refractive index guided semiconductor laser device, the loss inside of a cavity can be decreased, whereby high light output power is possible. When the semiconductor laser device is used in an optical pickup as a light source for a rewritable optical disc such as a magneto-optical disc or a phase change disc, however, realization of higher light output power of the semiconductor laser davice is required. In addition, when writing at more than fourfold speed, it is desired that with respect to the output power of the laser device, maximum light output power is not less than 70 mW in fundamental transverse mode lasing, and a horizontal beam divergence .theta..sub.H in the horizontal direction is not less than 6.5.degree. in order to reduce noise characteristics or the like in a case where the semiconductor device is carried by the optical pickup.